Control of constant current circuits



y 2, 1935- c. G. sun's 2,006,970

CONTROL OF CONSTANT CURRENT CIRCUITS Filed Sept. 25, 1935 Fig. I.

3 /Constant Current Transformer? Fig. 2.

Inventor; Chaunce g GSuits His A tornqg- Patented July 2, 1935 CONTROLOF CONSTANT CURRENT CIRCUITS Chauncey G. Suits, Schenectady, N. Y.,assignor to General Electric Company, a corporation or New YorkApplication September 23, 1933, Serial No. 690,704

4 Claims.

My invention relates to alternating current circuits of the constantcurrent type, including a source of constant current and a load suppliedthereby. It is the object of my invention to provide a circuit of thischaracter having improved means for causing regularly recurringvariations in the eiIective value of the current supplied to the load.

My invention will be better understood from the following descriptiontaken in connection with the accompanying drawing, and its scope will bepointed out in the appended claims.

Referring to the drawing, Fig. 1 is a circuit diagram of one embodimentof my invention; and 2 is a circuit diagram showing a modificationthereof.

In Fig. l I have shown at i a constant cu;- rent transformer which maybe of any well known form, such for example, as that commonly employedfor the supply of constant current lighting circuits. The primary 2 ofthis transformer is supplied from the constant potential source 3, 4 ofalternating current, which source may, for example, be a cycle, voltcommercial lighting circuit. The secondary 5 of the transformer connectswith the load circuit 8 which is shown containing a plurality of loaddevices I which may be are or incandescent lamps. A constant currentlighting circuit of this type is well known particularly in streetlighting systems employing arc lamps in which case the current suppliedis maintained commonly at a value of approximately 6.6 amperes; it willbe understood, however, that where the load devices or lamps require alower current suitable adjustments or changes in the construetion wouldbe made in the transformer so as to give the desired current in the loadcircuit.

For ordinary lighting purposes it is desirable that the lamps shalloperate to give a constant illumination, but in certain other caseswhere it is important that the lamps shall be readily distinguishablefrom other lamps in the vicinity, it is desirable that the light fromthe lamps shall undergo variations in intensity in some easilyrecognized manner. For example, if the light from the field border lampsof an airport is caused to vary in some regular manner a pilotapproaching the airport is at once able to dis-.

tinguish those lamps from 'all other lamps in the vicinity and therebylocate the landing field with less difllculty. Moreover each airport soequipped may have its field border lamps varied at a diflerentfrequency, thus facilitating the recognition of each particular port asdistingulshed from the other ports.

In accordance with my invention 1 have provided the load circuit withmeans for producing regularly recurring variations in the efiectivevalue of the alternating current supplied to the load, which means isentirely electrical in operation; that is, it has no relatively movingparts and operates in response to the electrical condition of the loadcircuit. For this purpose I have provided a variable shunting meansconnected across the load circuit whereby a variable portion of thecurrent supplied by the transformer is shunted around the load circuit.The shunting means which I have provided is the saturable core reactor 9having the saturating winding l 0 which reactor connects with the0pposite sides of the load circuit by the leads it. The currenttransformer I2 having its primary winding l3 connected in serieswith theload circuit has its secondary winding is connected to supplyalternating current to the non-linear resonant circuit l5 whichcomprises the capacitor IS, the resistor l1, and the self-saturatingreactor l8. In accordance with the value of the capacitance, resistance,and inductance in this circuit the circuit becomes resonant with apredetermined voltage supplied thereto by the secondary l4 and hence inaccordance with the value of the current supplied to the load sircuit.The circuit [5 therefore is a voltage sensitive non-linear resonantcircuit since the co dition of resonance in the circuit is dependentupon the voltage applied thereto. The current supplied to the saturatingwinding is of reactor 9 and hence the reactance produced by this reactoris varied in accordance with the current traversing the resonant circuitl5. Various means may be employed for energizing the saturating windingID to vary with the current in circuit 15. In Fig. 11 have shown thesaturating winding ID connected through the full wave rectifier l9 whichis arranged in series in circuit P5. In Fig. l I have representedreactor 9 in a purely diagrammatic manner; it will be understood,however, that this reactor may be of the form shown in Fig. 1 of myPatent 1,885,- 155, November 1, 1932, or if desired instead of employinga reactor having a single core I may employ two separate transformers asrepresented by Fig. 2 of the aforementioned pateht.

The operation of the apparatus shown in Fig. 1 will be readily apparentfrom the above description. Assuming that the current in the saturatingwinding l0 of reactor 9 is a mini-'- mum, the impedance offered by thereactor to the shunt circuit is a maximum, and hence maximum current isbeing supplied to the lamps I. When this maximum load current occurs thevoltage in the secondary ll of the current transiormer I2 is a maximum.The non-linear resonant circuit I5 is constructedto become resonant atthis maximum applied voltage and hence the current flow in the circuitl5 rises to a maximum and supplies a maximum current to the saturatingwinding it of the reactor. The re actor now becomes saturated in whichcondition the impedance ofiered thereby to the shunt circuit drops to aminimum; hence the current in the shunt circuit rises to a maximum.Since the transformer l is constructed to supply a constant current thecurrent which is not shunted by the reactor is insuflicient toilluminate lamps 1 to their full brilliancy or may be insufllcient evento make them visible. The resulting diminution in current in the loadcircuit now produces a diminished voltage applied to the non-linearresonant circuit l5 which diminished voltage is insumcient to preserve acondition oi resonance in that circuit. Accordingly the current suppliedto the saturating winding falls to the original minimum value. Thus thecycle or operation is completed. It will be understood that atimeelement is involved due to the well known characteristics ofsaturable core reactors, and in accordance with the particular apparatusemployed the number of light pulsations produced by the lamps 1 may varyover ,a considerable range, the periodicity of pulsation being in allcases materially less than the periodicity of the alternating currentsupply. It will be observed that the above described apparatus forcausing the variations in the load current is entirely electrical inoperation being devoid of 'any relatively? moving parts and being freefrom any interruption of the circuit where sparking may occur whichmight give rise radio interference.

In the modified form of my invention shown by Fig. 2, the non-linearresonant circuit is connected across the load circuit 6 whereby it isresponsive to the voltage supplied to the lamps rather than beingresponsive tothe current supplied thereto. In view of the closesimilarity of the operation of this form of my invention to that shownin Fig. 1 and described above, it is thought to be unnecessary to give adetailed explanation of the operation of this form.

I havev chosen the particular embodiments described above asillustrative of my invention and it will be apparent that various othermodifications may be made without departing from the spirit and scope ofmy invention which modifications I aim to cover by the appended claims.

What I claim as new and desire to secure by Letters Patent 01 the UnitedStates, is:

1. In combination, a constant current transformer, a load circuitconnected to be supplied therefrom, a saturable core reactor connectedto shunt said load circuit, and means including a voltage sensitivenon-linear resonant circuit constructed to pass from a non-resonant to aresonant condition, in response to a predetermined increase in currentin said load circuit for varying the saturation of said reactor.

2. In combination, a constant current transformer, a load circuitconnected to be supplied therefrom, a saturable core reactor providedwith a saturating winding and connected to shunt said load cn'cuit, acurrent transformer connected in the load circuit and a voltagesensitive non-linear resonant circuit connected to be energized fromsaid transformer and constructed to become resonant at a predeterminedvoltage supplied thereto for supplying current to said saturatingwinding.

3. In combination, a source of supply of alternating current, a lampcircuit, a constant current transformer connecting the source with thelamp circuit and means for causing the current in the lamp circuit toundergo regularly recurring variations, said means comprising asaturable core reactor provided with a saturating winding and connectedto shunt the lamp circuit, a transformer having its primary connected inseries in the lamp circuit, a voltage sensitive non-linear resonantcircuit including a selfsaturating'reactor connected to be supplied fromthe secondary of said transformer and constructed to become resonant ata predetermined voltage supplied thereto and a rectifier in saidnonlinear resonant circuit connected in circuit with said winding.

4. In combination, a constant current transformer, a load circuitconnected to be supplied therefrom, a saturable core reactor providedwith a saturating winding and connected to shunt said load circuit, avoltage sensitive nonlinear resonant circuit including a self-saturatingreactor connected across said load circuit whereby it becomes resonantwith a predetermined increase in current in the load circuit and meansincluding a rectifier for supplying curtrent to said winding from saidresonant circui CHAUNCEY G. SUITS.

